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Hybrid Orbitals

Hybrid Orbitals. With hybrid orbitals the orbital diagram for beryllium would look like this. The sp orbitals are higher in energy than the 1 s orbital but lower than the 2 p. Hybrid Orbitals. Using a similar model for boron leads to…. Hybrid Orbitals. …three degenerate sp 2 orbitals.

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Hybrid Orbitals

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  1. Hybrid Orbitals • With hybrid orbitals the orbital diagram for beryllium would look like this. • The sp orbitals are higher in energy than the 1s orbital but lower than the 2p.

  2. Hybrid Orbitals Using a similar model for boron leads to…

  3. Hybrid Orbitals …three degenerate sp2 orbitals.

  4. Hybrid Orbitals With carbon we get…

  5. Hybrid Orbitals …four degenerate sp3 orbitals.

  6. Hybrid Orbitals For geometries involving expanded octets on the central atom, we must use d orbitals in our hybrids.

  7. Hybrid Orbitals This leads to five degenerate sp3d orbitals… …or six degenerate sp3d2 orbitals.

  8. Hybrid Orbitals Once you know the electron-domain geometry, you know the hybridization state of the atom.

  9. Valence Bond Theory • Hybridization is a major player in this approach to bonding. • There are two ways orbitals can overlap to form bonds between atoms.

  10. Sigma () Bonds • Sigma bonds are characterized by • Head-to-head overlap. • Cylindrical symmetry of electron density about the internuclear axis.

  11. Pi () Bonds • Pi bonds are characterized by • Side-to-side overlap. • Electron density above and below the internuclear axis.

  12. Single Bonds Single bonds are always  bonds, because  overlap is greater, resulting in a stronger bond and more energy lowering.

  13. Multiple Bonds In a multiple bond one of the bonds is a  bond and the rest are  bonds.

  14. Multiple Bonds • In a molecule like formaldehyde (shown at left) an sp2 orbital on carbon overlaps in  fashion with the corresponding orbital on the oxygen. • The unhybridized p orbitals overlap in  fashion.

  15. Multiple Bonds In triple bonds, as in acetylene, two sp orbitals form a  bond between the carbons, and two pairs of p orbitals overlap in  fashion to form the two  bonds.

  16. Delocalized Electrons: Resonance When writing Lewis structures for species like the nitrate ion, we draw resonance structures to more accurately reflect the structure of the molecule or ion.

  17. Delocalized Electrons: Resonance • In reality, each of the four atoms in the nitrate ion has a p orbital. • The p orbitals on all three oxygens overlap with the p orbital on the central nitrogen.

  18. Delocalized Electrons: Resonance This means the  electrons are not localized between the nitrogen and one of the oxygens, but rather are delocalized throughout the ion.

  19. Resonance The organic molecule benzene has six  bonds and a p orbital on each carbon atom.

  20. Resonance • In reality the  electrons in benzene are not localized, but delocalized. • The even distribution of the  electrons in benzene makes the molecule unusually stable.

  21. Molecular Orbital (MO) Theory Though valence bond theory effectively conveys most observed properties of ions and molecules, there are some concepts better represented by molecular orbitals.

  22. Molecular Orbital (MO) Theory • In MO theory, we invoke the wave nature of electrons. • If waves interact constructively, the resulting orbital is lower in energy: a bonding molecular orbital.

  23. Molecular Orbital (MO) Theory If waves interact destructively, the resulting orbital is higher in energy: an antibonding molecular orbital.

  24. MO Theory • In H2 the two electrons go into the bonding molecular orbital. • The bond order is one half the difference between the number of bonding and antibonding electrons.

  25. 1 2 (2 - 0) = 1 MO Theory For hydrogen, with two electrons in the bonding MO and none in the antibonding MO, the bond order is

  26. 1 2 (2 - 2) = 0 MO Theory • In the case of He2, the bond order would be • Therefore, He2 does not exist.

  27. MO Theory • For atoms with both s and p orbitals, there are two types of interactions: • The s and the p orbitals that face each other overlap in  fashion. • The other two sets of p orbitals overlap in  fashion.

  28. MO Theory • The resulting MO diagram looks like this. • There are both s and p bonding molecular orbitals and s* and * antibonding molecular orbitals.

  29. MO Theory • The smaller p-block elements in the second period have a sizeable interaction between the s and p orbitals. • This flips the order of the s and p molecular orbitals in these elements.

  30. Second-Row MO Diagrams

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